Testosterone has significant effects in the body and affects everything from muscle mass, fat distribution, libido and mood. But it is not only the total amount of testosterone in the blood that is important. The circulating free and bioactive testosterone provides an even more nuanced picture of the hormone's true effects.
For increased knowledge of testosterone levels, we have developed a calculator based on the formula based on the medical publication The Journal of Clinical Endocrinology & Metabolism, Volume 84 issued October 1, 1999. The formula calculates the levels of free and bioactive testosterone based on total testosterone, SHBG in combination with albumin .
How to calculate free testosterone?
The traditional measurement of serum testosterone gives an overview of the total amount of hormone, but this measurement includes both active and inactive testosterone. For a more accurate assessment of testosterone's bioactive effects, specific calculations are needed that take into account the ratio between free, SHBG-bound and albumin-bound testosterone.
Such a calculation uses the values of total testosterone, SHBG and albumin to determine the free and bioactive fractions. Doing this will give you a more detailed understanding of your hormonal status.
The free form of testosterone
Free testosterone is a fraction of total testosterone that is not bound to any of the transport proteins albumin or SHBG. The free testosterone is therefore directly available to the cells, read more about the difference betweenfree and unbound testosterone . Calculations of free testosterone are recommended to be performed when analysis of total testosterone gives equivocal results. However, the test does not provide any diagnostic value when the fluctuations of the SHBG level are too high, SHBG values above > 170 nmol/L.
The reference value for free testosterone depends on sex, age and laboratory test methods, which means that different reference ranges are common.
| Age group | Men (nmol/L) | Women (nmol/L) |
|---|---|---|
| 17 - 40 years | 2.8 - 21 | 0.15 - 1.4 |
| 41 - 60 years | 2.0 - 15 | |
| > 60 years | 1.4 - 14 |
Why is the calculation of free and bioactive testosterone important?
The calculation can be of great importance in contexts where a person's symptoms do not correspond to the total testosterone levels. In such cases, a more detailed analysis may identify an imbalance that is not apparent when measuring total levels. This can create the basis for tailored treatment strategies that better address the individual's specific needs.
